Process for applying insulation to cables



United States Patent 3,167,610 PROCESS FOR APPLYING INSULATION T0 CABLES Thomas D. Cailinan, Yorktown Heights, N.Y., .assignor to International Business Machines Corporation, New York, N .Y., a corporation of New York No Drawing. Filed Dec. 27, 1961, Ser. No. 162,578 3 Claims. (Cl. 174-124) This invention relates to a method for insulating cables or the like and specifically to a method for applying tightly wound wrappings of insulating paper to a cable.

It is conventional in the prior art to insulate telephone cables, power cables and the like with paper. Well known processes include the application of wet paper pulp to the cable and drying the pulp in situ to form a highly porous, uniform coating. This coating may later be impregnated with dielectric insulating oils. Another common method for applying paper insulation is to helically wrap a paper tape around the length of the cable or conductor. The present invention is directed to an improvement in the latter type of winding method, i.e., to an improvement in methods for helically wrapping paper insulating tapes on conductors or cables.

in producing insulated cables by the helical wrapping of paper tape, it is desirable to obtain extremely tight winding of the tape about the conductor in order to insure effective insulation. It has been noted, however, that the helical windings of such tape often loosen after a period of time, even though the tape initially is wound quite tightly about the cable core. It has also been observed that loosening of windings will occur even where the paper tape insulation has been applied under tension according to prior art methods.

It has now been found that the loosening of helically wrapped paper insulating tape is due to the expansion and contraction of the paper under the influence of atmospheric humidity.

Accordingly, the present invention has for its object the production of permanently tight wrappings of helically wound paper insulating tape.

A furtherobject of the invention is the production of cables helically wrapped with paper insulating tape wherein the windings remain tight even after the cable has been exposed to high humidity conditions for extended periods of time.

The present invention comprises helically wrapping paper insulating tape about a core, such as a wire condoctor or cable, exposing the wrapped core to an atmosphere of high relative humidity for a number of hours and then permitting the treated wrappings to equilibrate with the atmosphere, thus producing wrappings that are premanently tight.

The invention will perhaps be better understood with reference to the following more detailed description of one embodiment of the method.

A high voltage electrical cable of approximately three inches in diameter is helically and loosely wrapped with a paper insulating tape by means of conventional tape wrapping apparatus. The paper tape employed is approximately 0.003 inch thick, approximately one inch wide and is of a high purity paper derived from the sulfate process treatment of wood pulp.

In the foregoing description the term loosely wound indicates that the paper insulating tape is wound on the cable under no tension and with no special attempt to secure tight windings. The windings are not loose in the sense that they may be easily slipped over one another or off the cable entirely, but are relatively loose as opposed to windings which are tensioned during application.

Next, the helically wrapped cable is introduced into a chamber at about room temperature, 25 C., in which the atmosphere is maintained at above 98 precent relative humidity and the Wrapped cable is maintained in this atmosphere for approximately 24 hours.

The treated cable is then removed from the high humidity chamber and is exposed or permitted to equilibrate at the prevailing humidity, percent relative humidity in this specific example, for a period of approximately 48 hours. Equilibrium is known to have been reached when the tape ceases to lose weight.

The period of time required for the tape to reach an equilibrium condition will depend upon the nature of the tape, the prevailing atmospheric conditions and other variable factors. The period could also be materially shortened, to as little as one hour, by application of a vacuum to remove water.

As a result of this treatment, the loose helical wrapping becomes permanently tight about the cable.

Lower humidity levels, other than the 98 percent relative humidity of the example, may also be employed with satisfactory results, but 98 percent produces good results with all types of insulating papers.

The results obtained according to this method may be explained by the fact that the paper insulating tape appears to undergo a permanent shrinkage as a result of the treatment.

Insulated cables obtained according to the foregoing method have been exposed over long periods of time to changing humidity conditions without any noticeable loosening of the wrappings.

Paper tapes of various dimensions and composition may be employed in the process with comparable results.

It should be clear that the paper insulation of th present method may be applied directly to the cable as the primary insulation or may be wound as an interlayer or top layer on a cable which has first been coated with rubber, varnish, glass fiber cloth or other insulating material.

It will also be apparent that various cables or cores may be substituted for the high voltage electrical cable employed in the detailed description of the method without departing from the scope of the invention.

Likewise, the time periods of high humidity exposure and equilibration may be adjusted to suit the nature of the particular paper used as the insulation without materially departing from the scope of the invention.

It is clear that the present invention is not limited to the specific steps and materials noted in the preferred embodiment and that those skilled in the art may conceive modifications of the invention Without departing from the scope of the following claims.

What is claimed is:

1. A method for producing tight, helical wrappings of paper tape insulation on cables comprising loosely and helically wrapping a cable with a paper insulating tape, exposing the loosely wrapped cable to an atmosphere of high relative humidity and then exposim the wrapped cable to atmospheric humidity conditions until the Wrapped cable reaches a state of equilibrium with the 3. The product obtained according to the method of atmosphere. claim 1.

2. A method for producing tight helical windings of paper tape insulation on a cable core comprising loosely References (lined in the file of this Patent and helically Winding paper insulating tape about the cable 5 core, exposing the wrapped cable to 98 percent relative UNITED STATES PATENTS humidity for 24 hours and then equilibrating the so treated 2 {)1 1 452 Lu'tz Aug 13 1935 wrapped cable at 50 percent relative humidity for 48 h'g'fgiiiilliiili 1956 hours. 

1. A METHOD FOR PRODUCING TIGHT, HELICAL WRAPPINGS OF PAPER TAPE INSULATION ON CABLES COMPRISING LOOSELY AND HELICALLY WRAPPING A CABLE WITH A PAPER INSULATING TAPE, EXPOSING THE LOOSELY WRAPPED CABLE TO AN ATMOSPHERE OF HIGH RELATIVE HUMIDITY AND THEN EXPOSING THE WRAPPED CABLE TO ATMOSPHERIC HUMIDITY CONDITIONS UNTIL THE WRAPPED CABLE REACHES A STATE OF EQUILIBRIUM WITH THE ATMOSPHERE.
 3. THE PRODUCT OBTAINED ACCORDING TO THE METHOD OF CLAIM
 1. 